1. Field of the Invention
This invention relates generally to systems and methods for sensing the condition of liquid in a tank or container. More particularly, embodiments of the present invention relate to sensing characteristics of automotive urea solution in a urea tank in a motor vehicle by propagating electromagnetic waves into a urea tank.
2. Description of the Prior Art
Selective Catalytic Reduction (SCR) vehicles, also referred to as Euro V vehicles, are diesel powered motor vehicles which are compatible with the use of an operating fluid to reduce emissions. Typically, the SCR vehicle has a urea tank, separate from the fuel tank, which is used to carry an operating fluid such as an automotive urea solution, or the like. Automotive Urea Solution (AUS) is a solution of high purity urea in de-mineralized water. AUS is stored in a urea tank of an SCR vehicle and is sprayed into the exhaust gases of the vehicle in order to convert oxides of nitrogen into elementary nitrogen and water. An SCR vehicle may then advantageously satisfy the Euro V Emissions Standard.
It is important for the Engine Management System (EMS) of an SCR vehicle to have information on the composition of the AUS, so that the EMS may adjust certain vehicle parameters to optimize vehicle performance, specifically emissions control.
In order to ensure this method of reducing emissions in an SCR vehicle remains effective, the quality of the AUS must be maintained. Contaminants, a change in the ratio of high purity urea to other constituents, temperature variation or other changes can impact the life expectancy of the AUS and the effectiveness of the AUS at reducing emissions.
SCR vehicles generally rely on the use of direct measurement systems to determine the level of AUS in a tank. Such systems typically comprise a plurality of sensors disposed at different levels along the vertical plane inside the urea tank. Such sensors typically have poor resolution, are intrusive, and do not detect the quality or temperature of the AUS. Such direct measurement systems also require installation of mechanisms inside the urea tank. Repair, replacement, or adjustment of such an internal direct measurement system is problematic. Furthermore, such systems are ineffective when employed in an SCR vehicle which is exposed to temperatures under minus eleven degrees centigrade, which is the temperature that AUS typically freezes, because such systems do not provide a means of measuring AUS temperature to enable the correct application of heat to prevent freezing of the AUS.
SCR vehicles generally rely on the use of indirect measurement systems to determine the effectiveness of the AUS in reducing vehicle emissions. Such indirect measurements are taken from the exhaust fumes and are passed to the EMS, whereupon the EMS may increase or reduce the quantity of AUS released from the tank. Such systems are typically slow to react and do not accurately reflect the actual quality or composition of the AUS.
Thus, the prior art fails to provide a reliable, inexpensive, and accurate system and method of measuring the level or quality of AUS in a motor vehicle urea tank, let alone both.